There has been growing interest in developing safe, high-power lithium ion batteries for transportation applications, such as hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV). Among the available portable energy storage solutions, lithium ion batteries have the highest energy density, and as a result, lithium ion batteries are a likely candidate for use in transportation applications. Yet, there are technical barriers for using lithium ion batteries in such applications.
Technological barriers related to the use of lithium ion batteries, include power capability concerns. As batteries decrease in size and cost, the power capability of the batteries must remain high. In other words, for a battery to find application as a transportation power source, the battery needs to exhibit a enough power capability to power the vehicles or accept energy from braking vehicles.
A certain amount of gas is generated inside a battery due to the interfacial reactions inside a lithium ion battery, such as formation of solid electrolyte interphases (SEI) during formation or decomposition of old SEI layers at elevated temperatures. The generation of gas may lead to a slow degradation of electrode materials, or a reduction in the active electrochemical surface area (i.e., an increase in impedance) by blocking the charge/ion transport pathways. When gas accumulates in a battery cell, the power capability of the cell is then concomitantly deteriorated. Nano-structured Li4Ti5O12 can be a safe negative electrode material with high power capability and capacity retention. However, significant amount of gas is observed at elevated temperatures when nano-structured Li4Ti5O4 was used against lithium manganese oxide spinels.